Building Embedded Linux Systems Introduction

Embedded Linux

Information Technology Institute (ITI)

Sherif Mousa

Embedded Linux @ Information Technology Institute 1

2– Introduction To Embedded Linux

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Definition

Embedded Linux @ Information Technology Institute

Definition

• Embedded Linux is the use of Linux in embedded computer systems.

• Adapting the Linux kernel and customizing the user-space libraries and utilities to embedded applications such as those in use in consumer electronics, military, medical, industrial, and auto industries.

• Creating an Embedded Linux based system is like a puzzle. Putting the right pieces together will create the final image.

Embedded Linux @ Information Technology Institute 3

4

Some Whys ???


Why Embedded ?

? 5 Embedded Linux @ Information Technology Institute

Why OS for Embedded ?

• Make use of micro-processor capabilities (Multi-Tasking …).

• Easy to program.

• System scalability.

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Why Embedded not Normal OS ?

• Systems with small and limited resources.

• Special-Purpose systems.

• Real-Time systems.


Why Linux ?

• Inexpensive, Robust, Easy to program.

• Source code is available.

• Ported to a variety of CPU architectures.

• Large device drivers coverage.

• Hosting huge number of languages & libraries.

• Software is highly modularized, making it easy to build something new.


Why build from scratch ?

• “When you bake it at the factory that’s what it does forever. “ Tim Bird, Sony Entertainment

• You can use ready-made distributions as well, but you will face some restrictions if you need to modify something.


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Some Facts


Is it easy ?

• NO, IT’S NOT EASY.

• To finish a complete OS, it’s not just Linux kernel to compile, you need to build and integrate the other OS components (BootLoader, Libraries, Commands, …….)

• And you will do all of this without getting a PhD degree in OS building


Do I need more knowledge ?

• If you are a Linux super user, and you think that you need to learn more things to enter the Embedded Linux field, THAT’S WRONG.

• Linux - Somethings = EmbeddedLinux


Android is embedded Linux?

• “Of course not” Karim Yaghmour

• Google custom-built Android as a mobile operating system that comes with its own ecosystem, separate from the classic Linux ecosystem. Its user interface is optimized for touch screen devices. It comes with a set of APIs. But most classic embedded devices don’t need Google maps, for example.


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Embedded Linux Development


Cross Compiler

• A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is running.


ToolChain

• Set of programming tools that are used to create a product (typically another computer program), used in chain.

• A simple software development ToolChain consists of a compiler and linker to transform the source code into an executable program, libraries to provide interfaces to the operating system, and a debugger.


Cross-ToolChain

• The usual development tools available on a GNU/Linux workstation is a native ToolChain.

• For embedded systems, it is usually impossible or not interesting to use a ToolChain installed on it – The target is restricted in terms of storage and memory

– The target is very slow compared to your workstation

• Therefore, Cross-ToolChain is used. They run on your workstation but generate code for your target.


Cross-ToolChain


X86 Binary Target Binary

X86

X86 Target CPU

Source Code

Native ToolChain Cross ToolChain

Cross-ToolChain Components

• Binutils is a set of tools to generate and manipulate binaries for a given CPU architecture – as, ld, ar, …….

• Kernel headers – Available system calls and their numbers, Constant

definitions, Data structures.

• C/C++ libraries – Interface between the applications and the kernel – glibc (or) uClibc

• GCC compiler • GDB debugger


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Embedded Linux Components



• Boot Loader (grub, Lilo, Uboot)

• Kernel (Normal or Real-Time)

• FileSystem (FHS)

• Configuration files

• C Library

• Common system commands

• User application(s)



• Bootloader – Started by the hardware, responsible for basic

initialization, loading and executing the kernel.

• Linux Kernel – Contains the process and memory management, network

stack, device drivers and provides services to userspace applications.

• System libraries (C library) – The interface between the kernel and the userspace

applications.

• Filesystem – Contains Linux commands, libraries and other needed

scripts.


System Integration & Installation

• Integrate all the components, bootloader, kernel, system libraries and applications and our applications into a full working system.

• Install the OS into the device (?!!??!?!!!?!?!)


Booting Sequence

• Bootloader – Executed by the hardware at a fixed location in ROM / Flash – Initializes support for the device where the kernel image is found

(local storage, network, removable media) – Loads the kernel image in RAM and execute.

• Kernel – Uncompresses itself – Initializes the kernel core and statically compiled drivers (needed to

access the root filesystem) – Mounts the root filesystem (specified by the root kernel parameter) – Executes the first userspace program (specified by the init kernel

parameter)

• First userspace program Configures userspace and starts up system services and user interface (if found).


Linux System Running


Hardware

Linux Kernel

User Space C Library

app A app B

Call a service

Manage Hardware

Event Handler

Event notification

Then What ???

• Once you have the system installed with no problems on your development device, you are free to write applications as you need with the any programming language (supported by your embedded OS).



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